Sigma C 65 mm f/2 DG DN
7. Coma, astigmatism and bokeh
| Center, f/2.0 | Corner APS-C, f/2.0 | Corner FF, f/2.0 |
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| Center, f/2.8 | Corner APS-C, f/2.8 | Corner FF, f/2.8 |
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Astigmatism, understood as an average difference between vertical and horizontal MTF50 function values, amounted to 6.1% and it is a slight level. It should be also noticed that the maximum relative aperture contributes the most to that result because by f/2.8 and by f/4.0 that aberration is reduced to practically zero.
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Defocused circles of light look well enough. Light spread in the circles is perhaps not as smooth as in case of fast portrait lenses but it doesn't give us any reasons to complain either. Neither a rim on the edge of the circle nor mechanical vignetting are especially bothersome; that last effect you can notice only in the area closest to the maximum relative aperture.
| Center, f/2.0 | Corner APS-C, f/2.0 | Corner FF, f/2.0 |
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| Center, f/2.8 | Corner APS-C, f/2.8 | Corner FF, f/2.8 |
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Center, f/4.0 | Corner APS-C, f/4.0 | Corner FF, f/4.0 |
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